1. Field of the Invention
The present invention relates to a method of manufacturing an organic EL panel, in which an EL (electroluminescence) element substrate having a plurality of EL elements formed thereon and an opposing substrate facing the EL element substrate are laminated together to form an organic EL panel.
2. Description of Related Art
Conventionally, organic EL (ElectroLuminescence) panels, one type of flat display device, have attracted attention as self-emissive display panels. An organic EL panel is produced by first forming a large number of EL elements on a glass substrate (an element substrate) by evaporation of various materials and then laminating an opposing substrate (cap glass, sealing substrate) onto an element forming surface of the element substrate. In such an organic EL panel, moisture must be excluded because the organic EL elements will significantly deteriorate if exposed to moisture. Further, in order to protect the organic EL elements from external damage, after formation of the EL elements, the opposing substrate is laminated onto the element substrate such that the EL elements are covered with the opposing substrate.
A method of manufacturing an organic EL panel according to the related art will be described with reference to FIGS. 1, 2A to 2D, 3A and 3B. First, an opposing substrate (cap glass) is prepared and a desiccant is applied to the opposing substrate (S1). More specifically, as shown in FIG. 2A, a desiccant 42 is applied to an etching pocket 64 formed on a panel region of the glass substrate 60 by etching. Then, the whole system is baked in an oven (S2). As a consequence, a solvent or the like evaporates from the desiccant 42 and the desiccant 42 is activated. Then, after cleaning a surface of the substrate 60 by UV irradiation (S3), a UV sealant is applied on the surface to form a UV sealing member 66 on planar portions surrounding the etching pocket 64, as shown in FIG. 2B. A region surrounded by this UV sealing member 66 corresponds to the panel region.
Next, as shown in FIG. 2C, an element substrate 10 is laminated on the cap glass 60 with a gap maintained between these two layers, while UV radiation is applied under pressure (S5). This lamination is carried out in a dry nitrogen gas (N2) atmosphere so that dry N2 is enclosed in a space surrounded by the UV sealing member 66 (a sealed space). At this point, EL elements are formed on the element substrate 10. More specifically, each organic EL element comprises an anode 12, an emissive element layer 20 having at least an emissive layer, and a cathode 14, which may be accumulated, for example, in that order, on the element substrate 10 made of glass or the like. The organic EL element has a passive matrix configuration in which the anodes 12 and the cathodes 14 are disposed in respective, orthogonal striped patterns with the emissive element layer 20 interposed therein between, or an active matrix pattern in which a thin film transistor or the like is provided for each pixel (not shown), and the anode 12 is individually formed for each pixel whereas the cathode 14 is formed as a common electrode for all the pixels.
While a region corresponding to only a single organic EL panel is shown in FIGS. 2A to 2D, when a plurality of panels are formed from a single large-size substrate, each of the cap substrate 60 and the element substrate 10 includes a plurality of panel regions which are partitioned from each other by a plurality of sealing members 66. Therefore, the cap glass 60 and the element substrate 10 which have been bonded together are cut into individual panels (S6) to thereby form the individual organic EL panels.
More specifically, as shown in FIG. 3A, a plurality of etching pockets 64, each corresponding to one of the individual organic EL panels, are formed in the cap glass (substrate) 60. Further, as shown in FIG. 3B, the thickness of the cap glass 60 is set to approximately 700 μm and the depth of the etching pocket 64 is set to approximately 300 μm.
It is also possible to inject silicon oil rather than enclosing dry N2 in the individual panels. When this is done, as in the case of a liquid crystal display, an injection opening 68 is formed in part of the UV sealing member 66 of an individual organic EL panel as shown in FIG. 2D, and the silicon oil is injected through the injection opening 68 into the interior space of the individual panel which has been cut (S7). After injection of silicon oil, the injection opening 68 is sealed (S8), and the organic EL panel is thus completed.
However, with the above-described configuration in which dry nitrogen is enclosed between the opposing substrate 60 and the element substrate 10, it is difficult to maintain a gap between the substrates in the sealed space where nitrogen only exists, and this may cause the opposing substrate 60 to come in contact with the elements and damage them when the opposing substrate 60 is deformed due to external pressure or the like. These problems are likely to occur as the panel size increases.
When silicon oil is injected, on the other hand, it is necessary to seal the injection opening formed in part of the UV sealing member 66 after injection, which complicates the assembly and manufacturing procedures.
Further, when dry nitrogen is enclosed between the opposing substrate 60 and the element substrate 10 according to the above-described manufacturing method, there is a possibility that an excessive amount of nitrogen gas may be enclosed in the sealed space, for example, due to misalignment in bonding the two substrates. Enclosure of excessive nitrogen would increase the pressure in the sealed space of the panel, leading to a problem that the opposing substrate 60 is likely to be unstuck from the element substrate.